Method and system for simultaneous detection of signed doppler shifts and range measurements

Abstract

A method and an apparatus for determining a signed Doppler frequency shift of an optical signal. The method comprises generating a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum; directing the transmission signal to at least one target; receiving a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum; estimating the reflection optical spectrum; and based on the estimated reflection optical spectrum and the reference optical spectrum, determining a signed Doppler frequency shift of the reflection optical spectrum, wherein at least one of the transmission optical spectrum and the reference optical spectrum comprises a first component having a first frequency and a first amplitude, and a second component having a second frequency, different from the first frequency, and a second amplitude, different from the first amplitude, and wherein the at least one of the transmission optical spectrum and the reference optical spectrum is asymmetric about the midpoint of the reference optical spectrum.

What is claimed is: 
     
         1 . A method of determining a signed Doppler frequency shift of an optical signal, the method comprising:
 generating a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum;   directing the transmission signal to at least one target;   receiving a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum;   estimating the reflection optical spectrum; and   based on the estimated reflection optical spectrum and the reference optical spectrum, determining a signed Doppler frequency shift of the reflection optical spectrum, wherein:   at least one of the transmission optical spectrum and the reference optical spectrum comprises a first component having a first frequency and a second component having a second frequency, different from the first frequency, and wherein the at least one of the transmission optical spectrum and the reference optical spectrum is asymmetric about the midpoint of the reference optical spectrum.   
     
     
         2 . The method of  claim 1 , wherein estimating the reflection optical spectrum comprises mixing the reflection signal with the reference signal, thereby generating a mixed signal, the method further comprising:
 detecting the mixed signal, thereby producing an electrical return signal corresponding to an intensity of the mixed signal, and wherein determining the signed Doppler frequency shift of the reflection optical spectrum is based on the electrical return signal.   
     
     
         3 . The method of any one of  claims 1  through  2 , wherein:
 generating the transmission signal comprises modulating a narrowband carrier signal by a first band-limited complex modulation signal, thereby producing the transmission signal, and wherein the transmission signal is broadband and has the transmission optical spectrum that is asymmetric about the midpoint of the reference optical spectrum. 
 
     
     
         4 . The method of any one of  claims 1  through  3 , wherein:
 generating the reference signal comprises modulating a narrowband carrier signal by a first band-limited complex modulation signal, thereby producing the reference signal, wherein the reference signal is broadband and has a reference optical spectrum that is asymmetric about the midpoint of the reference optical spectrum. 
 
     
     
         5 . The method of  claim 3  or  4 , wherein the first band-limited complex modulation signal is a frequency-modulated continuous wave chirp signal, a fixed-frequency continuous wave signal, or a combination thereof. 
     
     
         6 . The method of any one of  claims 1 - 5 , wherein estimating the reflection optical spectrum comprises applying a spectral estimation method to the electrical return signal. 
     
     
         7 . The method of  claim 6 , wherein the spectral estimation method is a Fourier transform. 
     
     
         8 . The method of  claim 6 , wherein the spectral estimation method is a time-frequency transform. 
     
     
         9 . The method of  claim 7 , wherein the spectral estimation method is a finite impulse response filter. 
     
     
         10 . The method of  claim 6 , wherein the spectral estimation method is a dynamic state-space phasor tracker. 
     
     
         11 . The method of  claim 6 , wherein the spectral estimation method comprises providing the electrical return signal to an artificial neural network. 
     
     
         12 . The method of any preceding claim, further comprising:
 based on the estimated reflection optical spectrum and the reference optical spectrum, additionally determining a range of the at least one target.   
     
     
         13 . The method of  claim 12 , wherein
 applying the spectral estimation method comprises determining a plurality of frequency components of the electrical return signal,   the method further comprising:   determining phases of the plurality of frequency components;   determining a range of the at least one target based on the signed Doppler frequency shift and the phases of the frequency components.   
     
     
         14 . The method of  claim 13 , wherein determining the range of the at least one target further comprises determining a range-related frequency shifts of the frequency components. 
     
     
         15 . An apparatus for determining a signed Doppler frequency shift of an optical signal, the apparatus comprising:
 a transceiver and a computing node in communication with each other,   the transceiver configured to, under the control of the computing node:
 generate a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum; 
 direct the transmission signal to at least one target; and 
 receive a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum; 
   the computing node configured to:
 estimate the reflection optical spectrum; and 
 based on the estimated reflection optical spectrum and the reference optical spectrum, determine a signed Doppler frequency shift of the reflection optical spectrum, wherein 
   at least one of the transmission optical spectrum and the reference optical spectrum comprises a first component having a first frequency and a second component having a second frequency, different from the first frequency, and wherein the at least one of the transmission optical spectrum and the reference optical spectrum is asymmetric about the midpoint of the reference optical spectrum.   
     
     
         16 . The apparatus of  claim 15 , wherein the transceiver module comprises a multiple frequency laser. 
     
     
         17 . The apparatus of  claim 15  or  claim 16 , further comprising a laser source configured to generate a narrowband carrier signal, wherein:
 the transceiver module further comprises one or more transmission quadrature amplitude modulators configured to generate a band-limited complex modulation signal and to modulate the narrowband carrier signal, thereby producing at least one of the transmission signal, wherein the transmission signal is broadband and has the transmission optical spectrum that is asymmetric about the midpoint of the reference optical spectrum, and the reference signal is broadband and the reference optical spectrum is asymmetric about the midpoint of the reference optical spectrum; 
 one or more optical detectors configured to generate an electrical return signal by mixing the reflection signal with the reference signal, thereby generating a mixed signal, and detecting the mixed signal, the electrical return signal corresponding to the intensity of the mixed signal; 
 the processor is further configured to:
 obtain a sequence of digitized samples of the electrical return signal; 
 apply a spectral estimation method to the digitized samples of the electrical return signal, thereby estimating the reflection optical spectrum; and 
 based on the estimated reflection optical spectrum, determining the signed Doppler frequency shift of the reflection optical spectrum. 
 
 
     
     
         18 . The apparatus of any one of  claims 15 - 17 , further comprising:
 a reference quadrature amplitude modulator configured to generate a second band-limited complex modulation signal and to modulate the reference signal by the second modulation signal.   
     
     
         19 . The apparatus of any one of  claims 15 - 18 , wherein the spectral estimation method is a Fourier transform. 
     
     
         20 . The apparatus of any one of  claims 15 - 18 , wherein the spectral estimation method is a time-frequency transform operator. 
     
     
         21 . The apparatus of any one of  claims 15 - 18 , wherein the spectral estimation method is a finite impulse response filter. 
     
     
         22 . The apparatus of any one of  claims 15 - 18 , wherein the spectral estimation method is a dynamic state-space phasor tracker. 
     
     
         23 . The apparatus of any one of  claims 15 - 18 , wherein the spectral estimation method comprises providing the electrical return signal to an artificial neural network. 
     
     
         24 . The apparatus of any one of  claims 15 - 18 , wherein the first band-limited complex modulation signal is a frequency-modulated continuous wave chirp signal, a fixed-frequency continuous wave signal, or a combination thereof. 
     
     
         25 . The apparatus of  claim 18 , wherein the second band-limited complex modulation signal is a frequency-modulated continuous wave chirp signal, a fixed-frequency continuous wave signal, or a combination thereof. 
     
     
         26 . The apparatus of any of  claims 15 - 25 , wherein the computing node is configured to:
 based on the estimated reflection optical spectrum and the reference optical spectrum, additionally determining a range of the at least one target.   
     
     
         27 . The apparatus of any of  claim 26 , wherein:
 applying the spectral estimation method comprises determining a plurality of frequency components of the electrical return signal,   the computing node being configured to:   determine phases of the plurality of frequency components;   determine a range of the at least one target based on the signed Doppler frequency shift and the phases of the frequency components.   
     
     
         28 . The apparatus of  claim 27 , wherein the computing node is further configured to determine the range of the at least one target further comprises determining a range-related frequency shifts of the frequency components. 
     
     
         29 . A method of determining a range to one or more targets by determining the round trip time-of-flight of an optical signal, the method comprising:
 generating a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum,   the reference optical spectrum having at least a first reference frequency component and the transmission optical spectrum having at least a first transmission frequency component and a second transmission frequency component, different from the first transmission frequency component;   directing the transmission signal to at least one target;   receiving a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum having first and second reflection frequency components that correspond to the first and second transmission frequency components;   mixing the reflection signal with the reference signal, thereby generating a mixed signal;   based on the mixed signal, estimating the reflection optical spectrum; and   based on the estimated reflection optical spectrum, determining a time-of-flight delay of the reflection signal,   wherein determining the time-of-flight delay of the reflection signal further comprises:   determining a representation of phase difference of frequency components in the mixed signal, said frequency components corresponding to interference of the first and the second reflection frequency components with the first reference frequency component; and   based on the representation of phase difference of frequency components in the mixed signal and on a difference of the frequencies of the first and second reflection frequency components, determining the time of flight delay of the reflection signal.   
     
     
         30 . The method of  claim 30 , further comprising detecting the mixed signal, thereby producing an electrical return signal corresponding to an intensity of the mixed signal,
 and wherein determining the time-of-flight delay of the reflection signal is based on the electrical return signal.   
     
     
         31 . The method of  claim 29  or  30 , wherein the frequency of at least one of the reference frequency component and the transmission frequency components are varied linearly in time (chirped). 
     
     
         32 . The method of  claim 35 , further comprising de-chirping the reflection signal. 
     
     
         33 . The method of any one of  claim 31  or  claim 32 , wherein the transmission signal is a fixed-frequency continuous wave signal, a frequency-modulated continuous wave chirp signal, or a combination thereof. 
     
     
         34 . The method of  claim 33 ,
 wherein the transmission signal is chirped, and   wherein determining the representation of the phase difference of the frequency components in the mixed signal comprises:   de-chirping the reflected signal; and   applying a spectral estimation method to the de-chirped reflected signal to identify the phases of the frequency components in the mixed signal.   
     
     
         35 . The method of  claim 34 , wherein the spectral estimation method is a Fourier transform,
 a time-frequency transform, a finite impulse response filter, or a dynamic state-space phasor tracker.   
     
     
         36 . The method of any one of  claims 29 - 35 , further comprising:
 generating a second reference signal having a second reference optical spectrum,   the second reference optical spectrum having at least a second reference frequency component;   mixing the reflection signal with the second reference signal, thereby generating a second mixed signal,   wherein determining the time-of-flight delay of the reflection signal further comprises:   determining a representation of phase difference of frequency components in the second mixed signal that correspond to interference of at least one of the first and second reflection frequency components with the second reference frequency component; and   based on the representation of phase difference of frequency components in the second mixed signal and on a difference between the frequencies of the first and second reflection frequency components, determining the time of flight of the reflection signal.   
     
     
         37 . An apparatus for determining a range to one or more targets by determining the round trip time-of-flight of an optical signal, the apparatus comprising:
 a transceiver and a computing node in communication with each other, the transceiver configured to, under the control of the computing node:   generate a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum, the reference optical spectrum having at least a first reference frequency component and the transmission optical spectrum having at least a first transmission frequency component and a second transmission frequency component, different from the first transmission frequency component;   direct the transmission signal to at least one target;   receive a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum having first and second reflection frequency components that correspond to the first and second transmission frequency components;   mix the reflection signal with the reference signal, thereby generating a mixed signal;   the computing node configured to:   based on the mixed signal, estimate the reflection optical spectrum; and   based on the estimated reflection optical spectrum, determine a time-of-flight delay of the reflection signal, wherein determining the time-of-flight delay of the reflection signal further comprises:
 determining a representation of phase difference of frequency components in the mixed signal, said frequency components corresponding to interference of the first and the second reflection frequency components with the first reference frequency component; and 
 based on the representation of phase difference of frequency components in the mixed signal and on a difference of the frequencies of the first and second reflection frequency components, determining the time of flight delay of the reflection signal. 
   
     
     
         38 . A method of determining a time-of-flight delay and signed Doppler frequency shift of an optical signal, the method comprising:
 generating a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum, wherein each of the reference signal spectrum and the transmission signal spectrum is time-varying at the same rate;   directing the transmission signal to at least one target;   receiving a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum;   estimating the reflection optical spectrum; and   based on the estimated reflection optical spectrum and the reference optical spectrum, determining a frequency shift of the reflection optical spectrum, the frequency shift having a Doppler shift component and a range shift component,   wherein:   at least one of the transmission optical spectrum and the reference optical spectrum comprises a first component having a first frequency, and a second component having a second frequency, different from the first frequency, and wherein the at least one of the transmission optical spectrum and the reference optical spectrum is asymmetric about the midpoint of the reference optical spectrums.   
     
     
         39 . The method of  claim 38 , further comprising:
 determining the range shift component of the frequency shift; and   based on the estimated reflection optical spectrum, the reference optical spectrum and the range shift component of the frequency shift, determining a signed Doppler shift component of the reflection optical spectrum.   
     
     
         40 . The method of  claim 39 , wherein determining the signed Doppler shift component of the reflection optical spectrum comprises subtracting the range shift component from the frequency shift. 
     
     
         41 . The method of  claim 39 , wherein:
 the reference optical spectrum has at least a first reference frequency component and the transmission optical spectrum having at least a first transmission frequency component and a second transmission frequency component, different from the first transmission frequency component; and   the reflection optical spectrum has first and second reflection frequency components that correspond to the first and second transmission frequency components, and wherein determining the range shift component comprises:   mixing the reflection signal with the reference signal, thereby generating a mixed signal;   based on the mixed signal, estimating the reflection optical spectrum; and   based on the estimated reflection optical spectrum, determining a time-of-flight delay of the reflection signal and thereby determining the range shift component, wherein determining the time-of-flight delay of the reflection signal further comprises:   determining a representation of phase difference of frequency components in the mixed signal, said frequency components corresponding to interference of the first and the second reflection frequency components with the first reference frequency component; and   based on the representations of phase difference of frequency components in the mixed signal and on a difference of frequencies of the first and second reflection frequency components, determining the time of flight delay of the reflection signal.   
     
     
         42 . The method of  claim 41 , further comprising detecting the mixed signal, thereby producing an electrical return signal corresponding to an intensity of the mixed signal, and wherein determining the time-of-flight delay of the reflection signal is based on the electrical return signal. 
     
     
         43 . An apparatus for determining a time-of-flight delay and a signed Doppler frequency shift of an optical signal, the apparatus comprising:
 a transceiver and a computing node in communication with each other,   the transceiver configured to, under the control of the computing node:
 generate a reference signal having a reference optical spectrum and a transmission signal having a transmission optical spectrum, wherein each of the reference signal spectrum and the transmission signal spectrum is time-varying at the same rate; 
 direct the transmission signal to at least one target; and 
 receive a reflection signal from the at least one target, the reflection signal having a reflection optical spectrum; 
   the computing node configured to:
 estimate the reflection optical spectrum; and 
 based on the estimated reflection optical spectrum and the reference optical spectrum, determine a frequency shift of the reflection optical spectrum, the frequency shift having a Doppler shift component and a range shift component, wherein: 
   at least one of the transmission optical spectrum and the reference optical spectrum comprises a first component having a first frequency and a second component having a second frequency, different from the first frequency, and wherein the at least one of the transmission optical spectrum and the reference optical spectrum is asymmetric about the midpoint of the reference optical spectrum.   
     
     
         44 . The apparatus of  claim 43 , wherein the computing node is further configured to:
 determine the range shift component of the frequency shift; and   based on the estimated reflection optical spectrum, the reference optical spectrum and the range shift component of the frequency shift, determine a signed Doppler shift component of the reflection optical spectrum.   
     
     
         45 . The apparatus of  claim 44 , wherein determining the signed Doppler shift component of the reflection optical spectrum comprises subtracting the range shift component from the frequency shift. 
     
     
         46 . The apparatus of  claim 42 ,
 wherein the reference optical spectrum has at least a first reference frequency component and the transmission optical spectrum has at least a first transmission frequency component and a second transmission frequency component, different from the first transmission frequency component, and   wherein the reflection optical spectrum has first and second reflection frequency components that correspond to the first and second transmission frequency components;   wherein the transceiver is further configured to mix the reflection signal with the reference signal, thereby generating a mixed signal;   wherein the computing node is further configured to:   based on the mixed signal, estimate the reflection optical spectrum; and   based on the estimated reflection optical spectrum, determine a time-of-flight delay and thereby the range shift component of the reflection signal,   and wherein determining the time-of-flight delay of the reflection signal further comprises:
 determining a representation of phase difference of frequency components in the mixed signal, said frequency components corresponding to interference of the first and the second reflection frequency components with the first reference frequency component; and 
 based on the representation of phase difference of frequency components in the mixed signal and on a difference of the frequencies of the first and second reflection frequency components, determining the time of flight delay of the reflection signal. 
   
     
     
         47 . The apparatus of  claim 46 , further comprising a detector configured to detect the mixed signal and to thereby produce an electrical return signal corresponding to an intensity of the mixed signal, and wherein determining the time-of-flight delay of the reflection signal is based on the electrical return signal.